1. Technical Field
The present invention relates to a liquid ejecting head unit which applies pressure fluctuation to pressure chambers communicating with nozzles so as to eject liquid in the pressure chambers through nozzles, such as an ink jet recording head.
2. Related Art
Liquid ejecting heads which cause pressure fluctuation on liquid in pressure chambers so as to eject the liquid through nozzles in a form of liquid droplets include an ink jet recording head (hereinafter, simply referred to as recording head) used in an image recording apparatus such as an ink jet recording apparatus (hereinafter, simply referred to as printer), a color material ejecting head used for manufacturing a color filter such as a liquid crystal display, an electrode material ejecting head used for forming an electrode such as an organic electro luminescence (EL) display and a field emission display (FED), a bioorganic compound ejecting head used for manufacturing a biochip, and the like, for example.
For example, as the above recording head, there is a recording head which is configured by attaching a flow path unit, an actuator unit, and the like to a head case made of a resin. A series of liquid flow path from a reservoir to nozzles through pressure chambers is formed on the flow path unit. The actuator unit has pressure generation elements which can change volumes of the pressure chambers. A nozzle plate on which a plurality of nozzles are opened is bonded to the flow path unit.
Viscosity of liquid to be ejected from such recording head, which is suitable for being ejected therefrom, is approximately 4 mPa·s at a normal temperature, for example. The viscosity of the liquid has a correlation with temperature. That is, as the temperature is lower, the viscosity tends to be higher. In contrast, as the temperature is higher, the viscosity tends to be lower. Further, for example, there is a case where the recording head is used for an application in which liquid in a so-called high viscosity region of equal to or higher than 8 mPa·s at the normal temperature, such as ultraviolet curable ink, is ejected, for example. Therefore, a recording head which includes a heater on a head case for heating liquid in order to set viscosity of liquid to be ejected through nozzles to a value suitable for being ejected regardless of an environmental temperature has been known. In addition, a recording head in which such heater abuts against a head cover for protecting a nozzle plate so as to transfer heat to the nozzle plate through the head cover so that liquid in the recording head is heated has been proposed (for example, see JP-A-2009-262543).
In the recording head as described above, when a distance of a flow path formed in the recording head is short (for example, when the recording head is small in size), liquid cannot be sufficiently heated because liquid flowing from the upstream side at the time of the liquid ejection passes through the recording head for a short period of time. In order to solve the problem, a liquid ejecting head unit having a configuration in which a heater is also provided on a flow path member located at the upstream side with respect to the recording head has been developed. However, in such liquid ejecting head unit, since a plurality of heaters are provided, a configuration thereof has become complicated and cost has been increased.